Spain is revisiting one of its darkest chapters in recent history as the trial gets under way of those accused in the March 11, 2004 Madrid train bombings that killed 191 people and wounded 1,824.

Of the 29 people on trial, seven -- including six alleged ringleaders and a man accused of supplying explosives -- face possible sentences of 38,000 years jail if found guilty.

The attacks, which have been linked to militant Islamic groups, including al-Qaeda, stunned Spain -- until then a staunch ally in the U.S.-led conflict in Iraq. Just three days later, the government was voted out of office and replaced with a new administration that withdrew Spanish troops from Iraq.